Electron emitter for electron tubes



July 28, 1953 P. D. WILLIAMS 2,647,067

ELECTRON EMITTER FOR ELECTRON TUBES Filed Sept. 10. 1949 n rowed m, /en

Q e i 7 INVE OR. PAUL L7. WILLIAMS BY M641 ATTORNEY UNETED Patented July 28, 1953 ELECTRON EMITTER- FOR ELECTRON TUBES Application September 10, 1949, Serial No. 114,958

1 Claim. (01. 117-3328) 1 My invention relates to an electron emitter or cathode for electron tubes, such as transmitting type vacuum tubes.

It is among the objects of my invention to profilaments.

Referring to the drawing:

clearly; and

filament.

onto the core.

type cathode.

hereinafter described in detail, a tubular metal anode 9 and a cage-like wire grid. Anode 9 has a cap 12 supported by a bracket l3 on lead l4 sealed to the upper end of the glass envelope.

The preferred pro- The preparation of the coating mixture As hereinbefore mentioned, the advanvide an emitter having the desired electron emis- 5 A pair of leads I! sealed to stem 3 support the sion properties of a thoriated type tungsten cathode, which leads are connected to a pair of emitter, but which is made from ordinary tungbase prongs I by conductors I8. The grid II has sten metal suitably treated rather than from the a base ring 2! supported by brackets 22 on a pair prepared thoriated tungsten heretofore employed. of rods 23 sealed to the stem 3, one of these rods Another object is to provide an emitter which being connected by a conductor 24 to the base may be fabricated in any suitable shape, includprong. Figure 2 shows the filamentary cathode ing surface type cathodes as well as wire type or emitter more clearly, the helical filament being connected at its ends to the leads I1. At the The invention possesses other objects and featime the filament is mounted on the leads H, the tures of advantage, some of which, with the foreglass stem 3 has not been sealed to the envelope going, will be set forth in the following descrip- 2, so that the filament stem assembly may be tion of my invention. It is to be understood that handled separat y from the remaining P t s I do not limit myself to this disclosure of species f the t during pr ing of the filament. of my invention as I may adopt variant embodi- My improved emitter of Figure 2 comprises a ments thereof within the scope of the claim. tungsten core wire coated with an intimate mixture of finely divided tungsten metal and thorium Figure 1 is an elevational view of an electron oxide sintered on the core. The tungsten used tube embodying a filamentary type cathode of for the core of the filament 8 may be an ordinary my invention, portion of the internal parts be- Commercial grade of substan ially pure tungsten ing broken away to show the structure more 25 wire and is suitably formed into helical shape and secured to the leads [1. Figure 2 is a detailed view showing the emitter Oedure n Comprises uc ori tungstate to a mixture of metallic tungsten and Interms of broad inclusion, my improved electhorium oxide, coating the tungsten core With tron emitter comprises a tungsten core, and a Such mixture, and s g e coating to the coating comprising an intimate mixture of tungcoresten and thorium oxide sintered on the core. from um tu t i an imp tan t p in The preferred method of making t tt the procedure, because it provides the desired comprises reducing thorium tungstate to a mixintimate mixture of Very fi y v ded t sten ture of tungsten and thorium oxide, coating the metal d thorium O core with the mixture, and sintering the coating Reduction of the thorium u sta is pref- Either wire or sheet-like core erably accomplished y placing a qu y f metal may be used, depending upon Whether t thorium tungstate powder in a suitable container emitter is to be of the filamentary or the surface and heating it in a yd atmosphere to a temperature of about 1000 C. This res lt i In greater detail and referrin to t drawing the partial reduction of the thorium tungstate a triode type of filamentary cathode tube is compound to metallic st and thorium chosen for purposes of illustration, it being un- Oxidederstood that my improved emitter may be intage of forming the mixture by this reduction corporated in tubes other than triodes. It is also pr s is th t t r s in p rtic s of t n sten understood that the emitter may be of the unimetal and thorium oxide are in a fi y divided potential urfa e type rather t t m state and are uniformly distributed to provide an mentary type shown. The tube illustrated comintimate mixture prises an evacuated glass envelope 2 with a stem The resulting p w ich is a fine black a carrying an exhaust tubulation 4 and provided w is t mixed with a liquid b d such with a base 6 having terminal prongs 1. Stem 3 as a yl acetate, to a Consistency Suitable for pis formed separately from the envelope 2 and is plication, as by spraying, on the core of fila t finally sealed to the envelope after the electrodes 8. A spray coat about .0005 inch thick on the have been mounted, as is conventional practice. wire core is satisfactory. The envelope encloses a filamentary cathode 8 The coated filament is then heated in vacuum to about 2300 to 2500" C. brightness temperature to sinter the coating. This sintering may conveniently be accomplished by passing current through the filament while the filament stem is in an evacuated bell jar. After sintering, the filament is carburized and otherwise treated in the usual manner of handling ordinary thoriated tungsten filaments.

For example, the filament is preferably carburized by heating it in a suitable hydrocarbon atmosphere to a temperature of say 2100 C. to 2400 C. brightness. The purpose of carburizing is to introduce carbon into the filament, by the formation of tungsten carbide, which carbon is then available for reducing the thoriumoxide to metallic thorium during operation of the filament.

After carburization, the grid 11 is mounted in place and the completed filament stem is sealed in the envelope. Thereafter, the tube is evacuated in the usual manner.

A hereinbefore mentioned, my improved emitter may be fabricated as a unipotential or surface type cathode. In this case a sheet of tungsten is used as the core instead of tungsten wire. A conventient shape is a cylinder of sheet tungsten having its outer surface coated as above described References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,608,317 Hyde Nov. 23, 1926 1,896,614 Gehrts Feb. '1, 1933 2,259,081 Felsner Jan. 6, 1942 2,339,392 Garner Jan. 18, 1944 2,438,732 Williams Mar. 30, 1948 2,447,038 Spencer Aug. 17, 1948 2,450,007 Litton Sept. 28, 1948 

